The invention relates to a lubricating system which includes a splash cooling of the pistons of an internal-combustion engine by means of spraying nozzles. The dissertation by Stefan Zima concerning the "Entwicklung schnellaufender Hochleistungsmotoren in Friedrichshafen" ("Development of High-Speed High-Efficiency Engines in Friedrichshafen"), Volume 2, 1984, Page 551, which was approved by Fachbereich 11 Konstruktion und Fertigung der Technischen Universitat Berlin (Technical Section 11 Construction and Manufacturing) of Technical University Berlin
In the initially cited dissertation by Stefan Zima, the cross-section of an internal-combustion engine is shown, in which the lubrication points at the crankshaft and at the connecting rods are supplied with lubricating oil through a central main duct to which the spraying nozzles for the cooling of the pistons are also connected. Lubricant ducts, which are separate in this respect and which are provided in the camshafts in the form of longitudinal bores, are used for feeding lubricating oil to the lubrication points at the camshafts and the valve timing gear of the internal-combustion engine. In internal-combustion engines, in which the spraying nozzles are connected to the main duct, the cooling of the pistons is interrupted after the start and during idling in order to have a sufficient amount of lubricating oil available for the lubricating of the lubrication points of the internal-combustion engine. For this purpose, control valves are used which stop the passage of the lubricating oil to the spraying nozzles as a function of the lubricant pressure, one control valve respectively being assigned to each spraying nozzle. Spraying nozzles of this type with assigned control valves are described, for example, in German Published Unexamined Application (DE-OS) No. 16 01 435. It is a disadvantage that the spraying nozzles combined with the control valves represent expensive components.
From German Patent No. (DE-PS) 27 20 034 it is known to assign the spraying nozzles for the cooling of the pistons to a separate lubricant duct which is used only for the feeding of cooling oil to the spraying nozzles. For the interruption of the cooling of the pistons, a single control valve is used by means of which the cooling oil supply to the lubricant duct and thus to all spraying nozzles is switched off simultaneously in the corresponding operating conditions of the internal-combustion engine. It is disadvantageous that a separate lubricant duct must be provided which is used only for the feeding of cooling oil to the spraying nozzles. In the narrow space conditions in modern engines, an additional lubricating oil duct, which extends along the whole length of the engine, as a rule, can be implemented only if other disadvantages are accepted.
An object of the invention is to ensure the lubrication of the main lubrication points of the internal-combustion engine during the starting phase, but using simple spraying nozzles without any integrated control valves for the cooling of the pistons and minimizing the overall expenditures for the system for the cooling of pistons
In the case of a device of this type, this object is achieved according to preferred embodiments of the invention by supplying the cooling nozzles with lubricating oil from lubricant ducts for supplying the camshafts and by providing that the amount of lubricating oil reaching the camshafts through the lubricant ducts is controlled as a function of engine operating conditions. In contrast to the other lubrication points of the internal-combustion engine, the supply of the lubricant to the lubrication points of the camshafts is not necessary with the exception of a small reduced quantity or even completely some time after the internal-combustion engine is started. The supply of a minimum amount of oil or the residual oil existing at the lubrication points of the camshafts ensures a sufficient lubrication. Therefore the feeding of the lubricating oil to the camshafts and to the spraying nozzles may take place by a joint lubricating oil duct, which, in the starting phase of the internal-combustion engine to the buildup of a sufficient lubricating oil pressure, contains an amount of lubricant that is reduced to a minimum or is separated completely from the lubricating oil supply system. The cooling of the pistons is not desirable in the starting phase, and also does not take place as a result of a lack of a sufficient feeding of oil. The interruption of the cooling of the pistons in operating conditions other than the starting phase is not necessary if the output of the lubricant pump is sufficient. An excessive cooling of the pistons during the idling operation of the internal-combustion engine cannot take place even if the cooling is not interrupted if, as customary in today's engines, the oil temperature is controlled by thermostats.
It is particularly advantageous that the spraying nozzles are no longer arranged in the central crankcase area above the crankshaft which is narrow in space and hard to reach, but that these spraying nozzles are now located in more easily accessible, less narrow lateral areas of the crankcase in which the camshafts are disposed.